1. Field of the Invention
The present invention relates to a throttle actuator for controllably moving the throttle of an automobile and the like between open and closing positions, and in particular to a throttle actuator which is under the control of both electric motor and wire.
2. Related Art of the Invention
Recently, automobiles have converted from means just intended for running from one place to another into means that rides easily or more comfortable vehicles. With the advent of such a need, various sorts of cruising systems are now being considered based on higher control technologies such as 4 wheel drive, 4 wheel steering, cruise control, etc. Among them, there is an attempt of obtaining cruising stability and safety, as well as low cost of fuel by the control of the throttle valve acting as a feed opening for fuel.
In a conventional car engine, the opening of degree of the throttle had only to act in response to the depression amount of an accelerator when it is pressed down. In this respect, the throttle valve and accelerator were mechanically connected with each other by means of a wire or link. As mentioned above, however, in many cases the throttle is now arranged such that it is electronically controlled for its opening dependent on the cruising conditions of the automobiles. Such an electronic control method has assisted developing of a cruise control function of keeping the running speed constant by regulating the output of an engine, TCS (traction control system) of preventing slipping of drive wheels by reducing the output of the engine, and ISC (Idle speed control) of controlling the rotational speed of the engine when idling takes place.
However, a variety of problems may result from attempts to bring the throttle under electronic control. The reason is as follows. There are different forms of approach to the electronic control of the throttle.
Specifically, it is an wholly electronically operable actuator that can make a control of the throttle. In this system, a throttle and an accelerator are quite independent from each other in mechanical terms with the structure that the depression amount of the accelerator may be read out by a sensor so as to drive the valve by a motor.
Another typical approach has an additional electronic control function with the mechanical connections reserved for operating the throttle valve by the use of the accelerator.
In comparison of the both above-described approaches, the former has an advantage that a small number of parts can do, that any mechanical connection is unnecessary, and that a single actuator can do, while the latter requires the mechanical connection and one (or two) actuator(s) as well.
In contrast, however, the former has a fault that it costs expensive. For example, provided only a cruise control is equipped as an optional function, an actuator such as an expensive stepping motor must indispensably be added in order to satisfy the cruise control function only, thus resulting in no substantial difference cost either if only one function is used or another function such as TCS is added to the function. With reference to the safety (fail-safe function) as a most important element, it is very difficult to secure the safety in the former system. Such being the case, it is considered to be unrisky that the mechanical system that has been used long with actual achievements in reliability is reserved.
Even so the latter, namely, the coexistence of mechanics and electronics tends to cause a complication in mechanism. FIG. 8 shows the conventional throttle valve having two valves provided within the body thereof. As shown in FIG. 8, this conventional example has a structure that one valve 80 is mechanically actuated by the accelerator and the other valve 82 is electronically controlled using a stepping motor 84, via a pinion 86 and a cam gear 88.
For example as the mechanics and electronics, another prior art is disclosed in Japan laid-open patent application No.64-12038. FIG. 7 shows this prior art. As shown in this drawing, if an accelerator 71 is depressed in the direction of an arrow A, a link member 73 is turned in the direction of an arrow B through a wire 72, and a throttle valve 75 is opened in the direction of an arrow C through a spring 74. With this state maintained, for an attempt to narrow the opening of the throttle valve 75 a little closer, the motor 76 is driven so as to be rotated by the shaft thereof in a direction D, and the link member 78 will be rotated through a connecting rod 77 in a direction E so that the throttle valve 75 may be closed by the spring 74 which is being compressed.
In the first prior art of FIG. 8, however, the throttle as a whole is inevitably of a large and heavy type due to its structure of two valves. The second prior art of FIG. 7 has a throttle that needs to transmit exact information of the degree of opening of the accelerator 71 generally during cruising, thus necessarily setting the spring 74 of an essentially strong resiliency. In this strong spring 74, if the throttle is to be actuated by the motor 76 to reduce speed, the spring 74 subjected to strong setting will have to be brought to more compression, with the result that a motor of a large type with a high torque is required. Additionally, since other specific mechanism is required to reduce the torque of the motor, the device will be of a mechanically bulky and complicated type.